This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 2000-065077, filed Mar. 9, 2000; and No. 2000-390832, filed Dec. 22, 2000, the entire contents of both of which are incorporated herein by reference.
The present invention relates to a rotary anode type X-ray tube, particularly, to an improvement of the bearing structure of the rotary anode type X-ray tube.
As known to the art, a rotary anode type X-ray tube comprises a disc-like anode target, a rotor and a stationary shaft. A bearing section is formed between the rotor and the stationary shaft, and the anode target is supported by the rotor and stationary shaft. An electromagnetic coil arranged outside a vacuum vessel receiving the rotor and stationary shaft is energized so as to rotate the rotor at a high speed. As a result, the electron beams emitted from the cathode are allowed to strike the anode target so as to achieve an X-ray emission.
The bearing section is formed of a roller bearing such as a ball bearing or a dynamic slide bearing in which helical grooves are formed in the bearing surface or section and a metal lubricant, which is in the form of a liquid during operation of the rotary anode-type X-ray tube, such as Ga or a Gaxe2x80x94Inxe2x80x94Sn alloy is supplied to the bearing surface.
The rotary anode type X-ray tube utilizing the slide bearing is disclosed in, for example, Japanese Patent Disclosure (Kokai) No. 60-117531, Japanese Patent Disclosure No. 2-227948, Japanese Patent Disclosure No. 5-13028, and Japanese Patent Disclosure No. 7-192666.
It is necessary to rotate the rotary anode type X-ray tube comprising a dynamic slide bearing using a liquid metal lubricant at a high speed, e.g., at 3,000 rpm to 8,000 rpm, during the operation. In addition, the X-ray tube tends to be inclined in an unspecified direction in many cases. However, it is necessary for the dynamic slide bearing section having helical grooves to be supplied with an appropriate amount of the liquid metal lubricant over a long time regardless of the posture assumed by the X-ray tube.
In a known rotary anode type X-ray tube, a space for storing the liquid metal lubricant, i.e., a lubricant reservoir, is formed of a fine hole extending along the axis of the stationary shaft. In this construction, however, the lubricant supply duct extending from the lubricant reservoir to the bearing section is rendered undesirably long, with the result that it is difficult in some cases to supply instantly the lubricant to a specified portion of the bearing depending on the posture assumed by the X-ray tube.
It is also known to the art that a relatively large space is formed in the outer circumferential portion of a stationary shaft portion having a large diameter and constituting a thrust bearing so as to provide a lubricant reservoir. In this construction, however, the lubricant within the lubricant reservoir receives a centrifugal force in accordance with rotation of the rotor, giving rise to the inconvenience that the lubricant is less likely to be supplied to the bearing section. As described above, a stable bearing operation is unlikely to be maintained in the prior art.
An object of the present invention is to provide a rotary anode type X-ray tube constructed to permit an appropriate amount of a liquid metal lubricant to be supplied with a high stability to the dynamic slide bearing section during operation of the X-ray tube.
According to a preferred embodiment of the present invention, there is provided a rotary anode type X-ray tube, comprising:
a substantially cylindrical rotor having an anode target fixed thereto;
a substantially columnar stationary shaft coaxially arranged inside the rotor so as to rotatably support the rotor;
a dynamic slide bearing having helical grooves and formed in the coupling portion between the rotor and the stationary shaft; and
a metal lubricant supplied to the helical grooves of the slide bearing and the bearing gap, the metal lubricant being in the form of a liquid at least during operation of the X-ray tube;
wherein an axial bore is formed in the columnar stationary shaft in a manner to extend in the longitudinal direction of the stationary shaft, and an insertion rod is inserted into the axial bore such that a space extending in the longitudinal direction of the stationary shaft is formed in at least a region between the inner circumferential surface of the axial bore and the outer circumferential surface of the insertion rod, the space acting as a lubricant reservoir for storing the metal lubricant.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.